Drug delivery by carbon nanotube arrays

ABSTRACT

The invention generally relates to carbon nanotube based drug delivery methods, devices, and compositions. More particularly, the invention relates to controlled drug delivery using anchored carbon nanotube arrays.

PRIORITY CLAIMS AND CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/224,287, filed Sep. 1, 2011, which claims the benefit of priorityfrom U.S. Provisional Application Ser. No. 61/379,701, filed Sep. 2,2010, the entire content of which is incorporated herein by reference inits entirety.

TECHNICAL FIELD OF THE INVENTION

The invention generally relates to carbon nanotube based drug deliverymethods, devices, and compositions. More particularly, the inventionrelates to controlled drug delivery using anchored carbon nanotubearrays.

BACKGROUND OF THE INVENTION

Targeted, localized and controlled drug delivery remains a majorchallenge. In many cases, efficacy of a drug can be improved and therisks of side effects reduced if the therapy is administered locallyand/or continuously, rather than through conventional oral ingestion orinjection, which produce burst releases. In some cases, dose-limitingtoxicity levels are caused by agent losses in vascular travel duringtransplant procedures. Continuous and accurate local dosing is highlydesirable, but remains a major challenge, particularly in thecardiovascular field where requirements for a material'sbiocompatibility and dosing control are stringent.

Current diffusion-based drug-delivery platforms suffer from very slowmass-transfer process. The published reports indicate involvement ofsolid/solid diffusion as well as channel (e.g., tubule) and solvent-help(e.g., capillary, osmotic) mechanisms but not convection. (Tepe, et al.2007 Touch Briefings 2007—Interventional Cardiology, pp. 61-63;Scheller, et al. 2004 Circulation 110:810-814; Diaz, et al. 2005 J BiolChem 280:3928-3937; Creel, et al. 2000 Circ Res 86:879-884; Lovich, etal. 2001 J Pharm Sci 90:1324-1335; Zilberman, et al. 2008 J Biomed MaterRes 84A:313-323; Davies 1997 N Engl J Med 336:1312-1314; Arakawa, et al.2002 Arterioscler Thromb Vase Biol 22:1002-1007; Parekh, et al. 1997 GenPharmac 29:167-172; Heam, et al. 2009 Nature 458:367-371; Celermajer2002 European Heart Journal Supplement F:F24-F28; Andersen, et al. 2006BMC Clinical Pharmacology, published online 13 Jan. 2006; Oreopoulos, etal. 2009 J Structural Biology 168:21-36; Panchagnula, et al. 2004 JPharm Sci 93:2-177-2183; Migliavacca, et al. 2007 Comput Methods BiomechBiomed Engin 10:63-73; Arifin, et al. 2009 Pharmaceutical Research,published online 29 Jul. 2009.) In percutaneous transluminal angioplasty(PCTA) devices, for example, drug washout and overdose remain seriouschallenges. For oncology applications, for example, localized deliveryof sufficient dose of anti-cancer drug via targeted delivery is highlydesirable.

In recent years, carbon nanotubes have attracted attention due to theirchemical, mechanical and geometric properties. Carbon nanotubes (CNTs)are allotropes of carbon with a cylindrical nanostructure and aremembers of the fullerene structural family. Nanotubes are categorized assingle-walled nanotubes and multi-walled nanotubes. Carbon nanotubes arestrong and stiff materials in terms of tensile strength and elasticmodulus respectively. Various techniques have been developed to makenanotubes, such as arc discharge, laser ablation, high-pressure carbonmonoxide, and chemical vapor deposition.

Researches have been reported on CNT-based drug delivery. For example, arecent study was reported on drug delivery using PEGylated-CNTs. (Liu,et al. 2008 Cancer Res. 68: (16), 6652). The reported system is based oncovalently attaching drug molecules to PEGylated CNTs. Another researchgroup used carbon nanotube-based tumor-targeted drug delivery system,which consisted of a functionalized CNTs linked to tumor-targetingmodules as well as prodrug modules. (Chen, et al. 2008 J Am Chem Soc130:16778-16785.) In both of the afore-mentioned approaches,functionalization of the CNTs is required, which presents a number ofcomplications and procedural drawbacks.

One reported example of angioplasty drug delivery is a PTCA ballooncoated with paclitaxel in an iopromide matrix. The balloon is inflatedfor 30-second contact with vascular wall to allow the matrix to dissolveand paclitaxel to migrate into the smooth muscle cell. (Scheller, et al.2004 Circulation 110:810-814.) Major problems with this device includeiopromide being hydrophilic and an X-ray contrast agent. The firstcauses some drug loss to blood stream (although claimed to be about 6%)and the second leads to adverse reactions for some patients.Furthermore, the balloon still contains about 10% paclitaxel afterdetachment and only about 15% remains in the plaque.

Another reported example of angioplasty drug delivery is a system usingvascular stents made of paclitaxel-eluting composite fibers to deliverabout 40% of drug, most of it over 30 days. (Zilberman, et al. 2008 JBiomed Mater Res 84A:313-323.) Since the main mass-transfer mechanism ofthis device is diffusion, the rate is inherently slow. These drawbacksare in addition to the well-documented risks and side effects associatedwith stents.

For angioplasty drug delivery monitoring, existing technologiestypically use a fluorescent dye administered intravenously through acentral venous line with a dose adapted to body weight. (Detter, et al.2007 Circulation 116:1007-1014; Hattori, et al. 2009 Circ CardiovascImaging 2:277-278; Hosono, et al. 2010 Interact CardioVasc Thorac Surg10:476-477; Tanaka, et al. 2009 J Thorac Cardiovasc Surg 138:133-140;Waseda, et al. 2009 JACC Cardiovascular Imaging 2:604-612.). Theillumination is provided by near-infrared laser diodes with a typicaloutput of 80 mW in a field of view of 10 cm in diameter, eliminatingtissue warming and eye protection concerns. The fluorescence emission ofthe excited dye is typically detected by an IR-CCD camera and digitizedwith a frame grabber that provides real-time recording.

Therefore, there remains an urgent and unmet need for improved drugdelivery systems addressing the above-mentioned shortcomings,particularly in the field of angioplasty drug delivery.

SUMMARY OF THE INVENTION

The invention is based, in part, on the unique approach to drug deliveryusing anchored carbon nanotube arrays. In particular, the inventionprovides targeted, localized, and controlled drug delivery using novelacnhored carbon nanotube arrays that carry (e.g., non-covalently) theagent to be delivered, including therapeutic and diagnostic agents.

In one aspect, the invention generally relates a method for deliveringan agent to a patient in situ. The method includes: (a) providing aplurality of carbon nanotubes; (b) depositing the agent to the pluralityof carbon nanotubes such that the agent is non-covalenty associated withthe plurality of carbon nanotubes; (c) placing the plurality of carbonnanotubes deposited with the agent at a target location in the patient'sbody; and (d) allowing the agent to diffuse from the plurality of carbonnanotubes, thereby delivering the agent in situ.

In another aspect, the invention generally relates to an implantabledrug delivery device. The implantable drug delivery device includes: (a)an implantable device; (b) an array of carbon nanotubes anchored on theimplantable drug delivery device; and (c) an agent deposited on thearray of carbon nanotubes, wherein the agent is not covalently bound tothe carbon nanotubes.

In yet another aspect, the invention generally relates to a method formonitoring in situ delivery of an agent. The method includes: (a)providing a plurality of carbon nanotubes non-covalently associatedthereon a pharmaceutical agent and a second agent capable of exhibitinga spatially detectable signal; (b) placing the plurality of carbonnanotubes at a target location in the patient's body; and (c) measuringthe detectable signal exhibited from the second agent to monitor thedelivery of the pharmaceutical agent in situ.

The invention disclosed herein enables improved devices, methods andcompositions for treating a number of conditions where targeted,localized, and controlled drug delivery are required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a)-(b) show an exemplary angioplasty-balloon fitted with carbonnanotubes. FIG. 1( c) and FIG. 1( d) are enlarged views of the carbonnanotubes.

FIG. 2 shows an exemplary carbon nanotube array prepared viacapillography methods.

FIG. 3 shows schematics of an array of anchored carbon nanotubes (astall as 1 mm) on a flexible substrate. (Sansom, et al. 2008Nanotechnology 19:035302; Sansom 2007 Ph.D. Thesis, California Instituteof Technology; Noca, et al. U.S. Pat. No. 7,491,628; Huang, et al. 2007Nanotechnology 18:305302; Gharib, et al. U.S. Pat. Appl. 20080145616A1.)

FIG. 4 shows exemplary surface-to-volume ratio comparisons of bundledanchored NTs and conventional microneedles. For the same total needlediameter of 50 μm, a bundle of ACNT has almost 100 times larger surfacearea than a conventional microneedle, assuming a modest CNT spacing of100 nm center-to-center. The uppermost line represents thesurface-to-volume gain by decreasing the CNT spacing by a factor of 2.

FIG. 5 shows a schematic drawing of anchored CNTs (as tall as 1 mm) withdrugs deposited in its interstices. (Zhou, et al. 2006 Nanotechnology17:4845-4853.)

FIG. 6( a) shows a flutax-coated anchored CNT array. FIG. 6( b) shows anuncoated CNT array.

FIG. 7( a) shows exemplary results of recovered fluorescein sodium andflutax-1 with the same initial concentration in DI water. FIG. 7( b)shows exemplary results of recovered fluorescein sodium with variousinitial concentrations in DI water.

FIGS. 8( a)-8(b) show a rubbing experiment using 3×1×5/128-inch glassmicroscopy slide rubbed on substrates made of CNT-fitted latex sheet(FIG. 8( a)) and bare latex sheet (FIG. 8( b)).

FIGS. 9( a)-(b) are exemplary images of 3×1×5/128-inch glass microscopyslides used in rubbing experiment. A significant amount of flutax-1 hasbeen washed-out from the substrate made of bare latex sheet in FIG. 9(a) and almost no flutax-1 washed-out from a substrate made of CNT-fittedlatex sheet in FIG. 9( b).

FIG. 10 shows exemplary recovered flutax-1 in pure ethanol after therubbing experiment, where the bare latex sheet shows that no moreflutax-1 remains (left) while much flutax-1 still remains on theCNT-fitted latex sheet (right); tubes OD=16 mm.

FIG. 11( a) shows an exemplary PET angioplasty balloon without CNTs.FIG. 11( b) shows a CNT-partially-fitted PET angioplasty balloon. Theblack region on the CNT-partially-fitted PET angioplasty balloon is anarray of vertically aligned CNTs anchored on latex, which cover theouter surface of the PET balloon.

FIGS. 12( a)-(b) show an exemplary experiment setup using agar gelinside a 860-μm-ID, 1,450-μm-OD glass capillary tube with a substratemade of CNT-fitted latex sheet (FIG. 12( a)) and bare latex sheet (FIG.12( b)).

FIGS. 13( a)-(f) are an exemplary series of time lapse images of masstransfer in 5 weight % agar gel, where the flutax-1 were transferred via˜300 μm CNT-fitted latex sheet (left) and bare latex sheet (right).

FIGS. 14( a)-(b) show an exemplary mass transfer profile of flutax-1 in5 weight % agar gel, where the flutax-1 were transferred via ˜300 μmCNT-fitted latex sheet (FIG. 14( a)) and bare latex sheet (FIG. 14( b)).

FIG. 15( a) shows a graph of location of 1% concentration vs. time for adried flutax-1 positioned as a shallow flat layer (squares, smooth line)and within and anchored CNT array (triangles, dashed line). The squaresand triangles mark experimental data and the dashed and smooth lines arenumerical solutions of the appropriate model. Schematic geometricdescriptions of the problem for a thin flutax layer and CNT array arepresented in FIG. 15( b) and FIG. 15( c), respectively.

DETAILED DESCRIPTION OF THE INVENTION

The invention is based in part on the discovery of a universaldrug-carrying and delivery platform capable of delivering targeted,localized, and controlled amounts of drugs to a target location within apatient's body. The devices, systems, methods and compositions of theinvention significantly remedy the difficult dose control problems incurrent PCTA devices as well as the complexity and costs associated withCNT functionalizations. Different from the common methods that have beenpublished earlier (e.g., Tepe, et al. 2007 Touch Briefings2007—Interventional Cardiology, pp. 61-63; Scheller, et al. 2004Circulation 110;810-814; Diaz, et al. 2005 J Biol Chem 280:3928-3937;Creel, et al. 2008 Circ Res 86:879-884), the device of the inventionincorporates a drug on CNTs without having to functionalize the CNTs.Conjugating drugs with functionalized CNTs is inherently complicated andexpensive. Additionally, the functionalizing process renders the CNTshydrophilic, such that the drug attached to the CNTs is vulnerable towashout by the blood stream. Additionally, as disclosed herein, theability to penetrate the arterial plaque cap and to deliver the drugsdirectly to the inner part of the plaque is a major advantage of aCNT-fitted angioplasty balloon over the conventional angioplasty-balloonor stent-fitted angioplasty balloon.

CNTs, since their discovery, have been studied for various applicationsranging from highly adhesive layers, heat sinks, structural composites,vibration damping layers, lithium storages, to field emitters, due totheir exceptional properties. (Iijima 1991 Nature 354; 56-58;Yurdumakan, et al. 2005 Chem Commun 30:3799-3801; Xu, et al. 2004 IEEEInter Society Conference on Thermal Phenomena 29:549-555; Veedu, et al.2006 Nature Materials 5:457-462; Daraio, et al. 2004 Appl Phys Lett85:5724-5726; Wang, et al. 2006 Metals and Materials Int'l 12:413-416;Manohara, et al. 2005 J Vac Sci Tech B23:157-161). The strength andflexibility of CNTs are just two of many exceptional physical propertiesof CNTs. The accepted Young's elastic modulus for individual CNTs isextraordinarily high, approaching 1 TPa (somewhat less for multi-walledCNTs than single-walled CNTs), which is almost 5 times higher thanstainless steel. (Wong, et al. 1997 Science 277:1971-1975, Krishnan, etal. 1998 Phys Rev B58:14013-14019.)

This high Young's modulus of elasticity allows the anchored CNTs topenetrate soft surfaces such as biological tissues upon touching andconsequently have the potential of delivering drugs directly to theinner part of the tissue. According to the linear elastic beam theory,the critical force for bucking of an axially loaded clamped cylindricalbeam in compression can be calculated by:

$F_{crit} = \frac{\pi^{3}{Ed}^{4}}{2\; S\; 6\; L^{2}}$

where d is the diameter of the beam, L is the length, and E is theYoung's modulus. Assuming a bundle of several CNTs is clamped togetheron the substrate, and typical diameter and length of a bundle of CNTsare 1 μm and 500 μm, respectively, the critical buckling force for eachbundle of CNTs is around 0.484 μN, or equivalent to 617 kPa. Thiscritical buckling force for each bundle of CNTs is great enough toovercome the required fracture stress of the arterial plaque cap, forexample, about 254.8 kPa. (Holzapfel, et al. 2004 J Bio Eng126:657-665.) As it is demonstrated herein, CNT bundles anchored on aflexible substrate are sufficiently strong to penetrate soft tissues,e.g. arterial wall or arterial plaque cap, when pressed upon and candeliver a drug directly to the inner part of these targets.

Another extraordinary property of CNTs that makes them a great fit fordrug delivery is the hydrophobicity of CNTs. By placing the drugs in theinterstices of an array of CNTs, the highly hydrophobic CNTs protect thedrugs from being washed out by any aqueous solution. Therefore, theCNT-fitted angioplasty balloon, for example, would protect the drugsfrom being washed-out during vascular travel to the target location.

Thus, in one aspect, the invention generally relates a method fordelivering an agent to a patient in situ. The method includes: (a)providing a plurality of carbon nanotubes; (b) depositing the agent tothe plurality of carbon nanotubes such that the agent is non-covalentlyassociated with the plurality of carbon nanotubes; (c) placing theplurality of carbon nanotubes deposited with the agent at a targetlocation in the patient's body; and (d) allowing the agent to diffusefrom the plurality of carbon nanotubes, thereby delivering the agent insitu.

In another aspect, the invention generally related to an implantabledrug delivery device. The implantable drug delivery device includes: (a)an implantable device; (b) an array of carbon nanotubes anchored on theimplantable device; and (c) an agent deposited on the array of carbonnanotubes, wherein the agent is not covalently bound to the carbonnanotubes.

In yet another aspect, the invention generally relates to a method formonitoring in situ delivery of an agent. The method includes: (a)providing a plurality of carbon nanotubes non-covalently associatedthereon a pharmaceutical agent and a second agent capable of exhibitinga spatially detectable signal; (b) placing the plurality of carbonnanotubes at a target location in the patient's body; and (c) measuringthe detectable signal exhibited from the second agent to monitor thedeliver of the pharmaceutical agent in situ.

In certain embodiments, the agent is a pharmaceutical agent capable ofproviding a therapeutic effect on the patient. Exemplary pharmaceuticalagents include: adrenaline (epinephrine), amphetamine, atropine taxol(or its fluorescent derivative flutax-1), and statins.

In certain other embodiments, the agent is a diagnostic agent capable ofproviding a detectable signal or image indicating a biologicallyrelevant state of the subject. Exemplary diagnostic agents include:electrochemical detectors of chemical warfare agents, utilizing superiorelectrical properties of carbon nanotubes.

In certain preferred embodiments, the agent comprises an aromatic moiety(e.g., arenes and heteroarenes). The aromatic moiety may include one ormore heteroatoms selected from N, O and S. The aromatic moiety mayinclude a single aromatic ring or two or more independent or fusedrings. The agent may be mono-aromatic or multi-aromatic.

In certain embodiments, the agent comprises a non-aromatic extendedπ-bond system.

Preferably, the agent may have a molecular weight from about 130 toabout 1500 (e.g., from about 130 to about 1200, from about 130 to about1000, from about 200 to about 1500, from about 200 to about 1200, fromabout 200 to about 1000, from about 500 to about 1000).

In certain preferred embodiments, the plurality of carbon nanotubes arein an array format and anchored on an implantable device. In certainpreferred embodiments, the plurality of carbon nanotubes are not surfacefunctionalized, e.g., for covalent attachment.

In certain preferred embodiments, the implantable device is anangioplasty balloon.

The angioplasty balloon is preferably anchored uniformly with theplurality of carbon nanotubes, e.g., without surface functionalization.The density of the plurality of carbon nanotubes is typically from about10¹⁰ nanotubes/cm² to about 10¹¹ nanotubes/cm² (e.g., about 2×10¹⁰nanotubes/cm², 4×10¹⁰ nanotubes/cm², 6×10¹⁰ nanotubes/cm², 8×10¹⁰nanotubes/cm².) (FIGS. 1( a)-(d)).

In a preferred embodiment, the agent is an agent for treating arterialplaque and the target location is interior wall of a vascular lumen ofthe patient. In some embodiments, the target location is inside anarterial plaque whereby at least some of the carbon nanotubes penetratethe outer lining and enter the interior of an arterial plaque.

The carbon nanotubes may be prepared by my suitable means, e.g., bythermal chemical vapor deposition. In some embodiments, the carbonnanotubes are multi-walled. In some embodiments, the carbon nanotubesare single-walled. The desired specifications of carbon nanotubes aredependent on the applications including the requisite strength of thenanotubes.

In certain embodiments, the agent is deposited to the carbon nanotubesby a method that includes: mixing the agent in a low surface tensionsolvent forming a solution of the agent; coating the plurality of carbonnanotubes with the solution of the agent; and drying the coatedplurality of carbon nanotubes, thereby removing the solvent whileleaving the agent associated with the plurality of carbon nanotubes.

The low surface tension solvent may be any suitable solvent, forexample, an alcohol. In certain preferred embodiments, the low surfacetension solvent is pure (200 proof) ethanol or another water-freealcohol.

The drug load is determined according to the requirements of theapplication. Drug load may range from about 0.1 mg to about 20 mg (e.g.,from about 0.1 mg to about 10 mg, from about 0.1 mg to about 5 mg, fromabout 0.1 mg to about 2.5 mg, from about 1.0 mg to about 20 mg, fromabout 1.0 mg to about 10 mg.)

CNTs can be formed in several ways, a simple way being a CVD method witha catalyst-coated substrate (typically a few nanometers of iron coatedonto silicon wafer) prepared in advance and placed in a tube furnaceunder saturated flow of carbon containing feed-gas (e.g., ethylene)small portion of reducer feed-gas, e.g. hydrogen, and elevated to propertemperature (e.g., 725° C.). Thermal CVD growth of CNTs in this waygenerates vertically aligned CNTs on the growth substrate. (Sansom, etal. 2008 Nanotechnology 19:035302; Sansom 2007 ExperimentalInvestigation on Patterning of Anchored and Unanchored Aligned CarbonNanotube Mats by Fluid Immersion and Evaporation, Ph.D. Thesis,California Institute of Technology.)

Various methods and techniques have been developed that allow thepreparation of anchored CNTs, including microscale fluid transport andcontrol techniques by “nanowicking” and by self-assembly patternformation and a method for controllable anchoring of CNTs within polymerlayers (Sansom, et al. 2008 Nanotechnology 19:035302; Sansom 2007Experimental Investigation on Patterning of Anchored and UnanchoredAligned Carbon Nanotube Mats by Fluid Immersion and Evaporation, Ph.D.Thesis, California Institute of Technology; Zhou, et al. 2006Nanotechnology 17:4845-4853; U.S. Pat. No. 7,491,628 Noca, et al.;Huang, et al. 2007 Nanotechnology 18:305301; U.S. Pat. App.20080145616A1 by Gharib, et al.). Tall CNT arrays have been grown inarbitrary patterns (e.g., bundles, rows, geometric shapes) on asubstrate with heights of over 1 mm (Bronikowski 2007 J Phys Chem C111:17705-17712.)

In contrast to the length of CNTs that can be varied relatively easilyby varying either the thickness of catalyst layer or the growth time,the packing density of an array of CNTs is relatively harder to vary.One way to adjust the packing density of the CNTs is by changing thetiming and duration of the hydrogen exposure during the CNT growth.(Nessim, et al. 2008 Nano Lett 8:3587-3593.) By this method, the packingdensity of as-grown CNTs can be varied from 3.9×10⁹ to 4.9×10¹⁰CNTs/cm². Another approach is by compressing the as-grown CNTs byexternal mechanical force or capillary force. (Wardle, et al. 2008 AdvMater 20:2707-2714; Futaba, et al. 2006 Nature Material 5:987-994). Byusing an external mechanical force to compact the as-grown CNTs, thepacking density of CNTs can be increased up to about 20%. By using acapillary force to collapse a pack of CNTs, the packing density of CNTscan be increased up to about 50%, or equivalent to the increase ofpacking density from 4.3×10¹¹ to 8.3×10¹² CNTs/cm².

A major challenge for the vertically aligned CNTs is the poor adhesionof the CNTs to their growth substrates, e.g., silicon wafer. Althoughthe mechanical properties of individual CNTs are excellent, thecollective properties of bulk vertically-aligned CNTs have not been asgood as expected, because of the weak bond between the base of the CNTsand their growth substrates. A method has been developed to overcomethis problem by anchoring the CNTs in a layer of flexible polymericmaterials, e.g., PDMS (polydimethylsiloxane), PMMA (poly(methylmethacrylate)), or latex, (Sansom, et al. 2008 Nanotechnology19:035302.) As-grown CNTs are manipulated by handling their growthsubstrate, inverted into a spin-coated polymer layer, and the assemblyis cured (usually by heat). (FIG. 2).

The CNT's growth substrate may then be removed. The CNT-growth can bepatterned by controlling the patterning of the thin iron catalyst layerprior to the CNT-growth step. Through separate control of polymer layerthickness and CNTs length, the depth of anchoring of the CNTs into theflexible polymer layer can be controlled. Thus, any pattern of as-grownCNTs, defined by catalyst pattern may be inverted and anchored into apolymer layer as required.

CNTs anchored in PDMS can withstand the shear stress up to 230 dyne/cm²and tensile stress up to 64.5 kPa. (Sansom, et al. 2008 Nanotechnology19:035302.). The effective adhesion strength between the CNTs and theflexible polymeric layer depends on the depth of anchoring of she CNTsinks the polymer layer, the strength of the bond between CNTs and thepolymer layer, and the fracture toughness of the polymeric layer.

Anchored CNTs on a flexible polymeric layer can be designed and preparedsuch that they have the requisite mechanical strength ensuring that noCNTs would enter the blood circulation or be left in the living tissuesthat may pose harm to the patient. The biocompatibility of CNTs has beendemonstrated, including evidences that show various types of livingceils (e.g. neuronal cells, osteoblast cells and fibroblast cells) canbe supported by CNTs (Hu, et al. 2004 Nano Lett 4:507-551; McKenzie, etal. 2004 Biomaterials 25:1309-1317; Webster, et al. 2004 Nanotech15:48-54; Gabay, et al. 2005 Physica A 350:611-621; Price, et al. 2005Biomaterials 24:1877-1887; Elias, et al. 2002 Biomaterials 23:3279-3287;Correa-Duarte, et al. 2004 Nano Lett 4:2233-2236.) Some studies havebeen reported that CNTs may present certain health problems, especiallyrelated to lung toxicity, cytotoxicity, and skin irritation. (Huczko, etal. 2001 Fullerene Sci Tech 9:247-250; Huczko, et al. 2001 Fullerene SciTech 9:251-254; Huczko, et al. 2005 Fullerene Nanotubes CarbonNanostruct 13:141-145; Lam; et al. 2004 Toxicol Sci 77:126-134; Warheit,et al. 2004 Toxicol Sci 77:117-125: Muller, et al. 2005 Toxicol AppPharmacol 207:221-231; Shvedova; et al. 2003 J Toxicol Environ Health A66:1909-1926; Monteiro-Rivtere, et al. 2005 Toxicol Lett 155:377-384;Jia, et al. 2005 Environ Sci Technol 39:1378-1383; Cui, et al. 2005Toxicol Lett 155:73-85; Tamura, et al. 2004 Key Eng Mater254-6:919-922.) Thus, to minimize the risk of side effects, the minimummechanical strength of the ACNT on a CNTs-fitted drug delivery systemmust be sufficiently higher than the maximum shear stress induced by thetissue.

Diffusion is an important mechanism in delivering drugs from anypharmaceutical system. The release kinetics of a drug delivery systemdepends on the initial concentration of the drug and the surface area ofthe system. Therefore, to improve the drug delivery mechanism, it iscrucial for a system to have a sufficiently large surface area. Such asystem can essentially be made by fitting an array of anchored CNTarrays onto a flexible substrate (FIG. 3).

The following expression compares the surface area of a CNT-fittedflexible substrate with a bare flexible substrate withoutCNT-enhancement.

$\frac{A_{{CNT}\text{-}{fitted}\text{-}{substrate}}}{A_{{bare}\text{-}{substrate}}} = {\frac{\frac{2\sqrt{3}\pi \; {dhWL}}{3\; s^{2}}}{WL} = \frac{2\sqrt{3}\pi \; {dh}}{3\; s^{2}}}$

Where d is the diameter of individual CNTs, h is the length ofindividual CNTs, s is the distance between individual CNT, W and L arethe width and length of the flexible substrate respectively. Using thefollowing assumed typical values, where d=10 nm, s=100 nm, and h=500 μm,the following result is obtained:

$\frac{A_{{CNT}\text{-}{fitted}\text{-}{substrate}}}{A_{{bare}\text{-}{substrate}}} = 1813.17$

This indicates that for a CNT-fitted drug delivery platform, themass-transfer surface for delivering drugs is about 1,800 times greaterthan that of a non-CNT-fitted platform of similar geometry. Therefore,there is a substantial increase in drug mass transfer rate when a drugdelivery platform is fitted with CNTs.

Compared to a simple hollow microneedle, the surface-to-volume ratio ofan anchored CNT bundle is at least one order of magnitude greater (FIG.4). This is again crucial for a local drug delivery platform. This largesurface-to-volume ratio also shows that a high dose of drugs can beplaced in a small size of CNT-fitted drug delivery platform.

The drug depositing technique for depositing drugs to CNTs may be anysuitable method. A novel approach disclosed here is to use a very lowsurface tension liquid (e.g., substantially lower than 72 dyne/cm(water, 25° Celsius), such as isopropanol, ethanol and acetone) to placethe drugs on the CNTs. Fluid transport based on wicking through anano-fibrous material has been previously studied and characterized.(Zhou, et al. 2006 Nanotechnology 17:4845-4853.) The same phenomenon isemployed here for depositing the drugs in the interstices of theanchored CNT array from their solutions followed by thorough drying(FIG. 5). Using this technique, anchored CNTs were coated with bothflutax-1 and uranine (sodium salt of fluorescein) (FIGS. 6( a)-(b)).

The drug depositing technique disclosed herein is a straightforward andless expensive method to place drugs within an anchored CNT array. Usingthis method, drugs can be placed in an anchored CNT array without havingthe need to functionalize the surface of the CNTs. Generally speaking,this method works preferably for drugs that have one or more aromaticmoieties and/or extended π-bond systems such as atropine andamphetamine, which help with the creation π-π interactions with CNTs. bycreating strong π-π interactions, the need to functionalize the CNTbeforehand is eliminated. Reduced surface tension liquids (optionallyhaving a surfactant such as sodium dodecyl sulfate (SDS) and similardetergents) easily wicked through CNT arrays. For example, a device canbe deposited with the drugs in the interstices of CNTS using an ethanolsolution of the drug followed by thorough drying to remove the solvent.

By attaching a flourescent molecule to the drug, e.g., taxol, directphotographic observation and monitoring of its movement into plaque canbe accomplished, for example, using fiber-optic-based technology andcalibration methods. (U.S. Pat. No. 5,116,317 by Carson, et al.; U.S.Pat. No. 4,842,390 by Sottini, et al.; Tepe. et al. 2007 Touch Briefings2007-Interventional Cardiology, pp. 61-63; Scheller, et al. 2004Circulation 110:810-814.) Substantial increases in drug mass tranferrate can be achivied when the angioplasty balloon is fitted withanchored CNTs, as disclosed herein.

In one embodiment, flutax-1 (i.e., a conjugated paclitaxel andfluourecein) is used. (Diaz, et al. 2005 J Biol Chem 280:3928-3937;Creel, et al. 2000 Circ Res 86:876-884; Lovich, et al. 2001 J Pharm Sci90:1324-1335.) Using flutax-1 allows measurement of pclitaxel deliveryto an arterial-plaque, optically and directly. This eliminates the needfor currently popular high-performance liquid chromotography (HPLC)approach that would need biopsy, or for ³H radio-labeled paclitaxelmeasurement. (Creel, et al. 2000 Circ Res 86:879-884.) Fabrication ofthis device is translatable to industrially scalable processes like toll-to-toll manufacturing for combining CNTs on substrates and plymerlayers that allows for very low-cost production.

The studies disclosed herein include micromechanics and nano-dynamicsrelevant to insertion mechanism of nanostructures into model tissues anddirectly-on-target interstitial mass-transfer phenomena involved withsuch insertion. The ability to penetrate the arterial plaque cap anddeliver the drugs directly inside the plaque is clearly an outstandingadvantage of a CNT-fitted angioplasty balloon over the conventionalangioplasty-balloon or stent-fitted angioplasty balloon.

Other studies disclosed herein relate to the prevention of the carrieddrugs from being rubbed-out/washed-away during procedure/travel to thetarget location. It is important to note that, due to the hydrophobicnature of CNTs, aqueous media such as blood plasma do not easily reachthe interior spaces of the CNTs where the drug. Is deposited. Byminimizing drug loss, the risks of overdosing patients may be reducedconsiderably, another outstanding advantage of an anchored CNT-fittedangioplasty over other drug-delivery devices. Studies and resultsdisclosed herein provide critical information needed tor fabricatingspecific-target drug delivery platforms and for guiding the developmentof novel drug delivery systems requiring access to interstital spaces.

Drug protection experiments were conducted to show that the CNTs protectthe deposited drugs from being washed away by blood-like liquids. Twotypes of dyes were used in these experiments, the fluorescein sodiumthat represents the hydrophilic drugs and flutax-1 that represents thehydrophobic drugs. Two types of specimens were used, a bare sheet oflatex and a sheet of latex with CNTs anchored on one side. Since theCNTs are highly hydrophobic, both fluorescein sodium and flutax-1 weredissolved in ethanol so that both dyes could go into the interstices ofthe CNTs. The same amounts of both fluorescein sodium and flutax-1 wereput in each specimen and allowed to dry. After the dye dried, eachspecimen was placed in 2 mL of DI water (to simulate blood) and theconcentration of the dye was analyzed using spectrophotometer.

The results showed that the hydrophobicity of CNTs protected thedeposited drugs, which could not be easily washed out by DI water. Onthe contrary, the DI water was able to wash out the fluorescein sodiumeasily (FIG. 7( a)). Notice the obvious difference of the recoveredamount of fluorescein sodium between the bare latex samples and theCNT-fitted latex samples. The bare latex samples lost almost all oftheir initial concentration of fluorescein sodium, while the CNT-fittedlatex samples retained about 50% of their initial concentration of thefluorescein sodium.

Another set of experiments was done using various concentrations offluorescein sodium on both types of specimens (FIG. 7 (b)). The time towash out the fluorescein sodium in DI water for the CNT-fitted latexsamples depended on the initial concentration. Lower initialconcentration lead to longer time that was needed to wash out thefluorescein sodium. This was not observed with the bare latex samples.The bare latex samples could not retain the fluorescein sodium frombeing washed away by DI water for whatever the initial concentrationwas.

Another experiment was performed that targeted possible drug removalfrom CNT-fitted drug delivery platform by mechanical (e.g., rubbing)actions during its cardiovascular travel. Two types of specimens wereused, a bare sheet of latex and a sheet of latex with CNTs anchored onone side. On each specimen, approximately 125 μg of flutax-1 wasdeposited by successively dropping small volumes of its ethanol solutionand allowed to dry. Next, 1 μL of DI water followed by a microscopic3×1×5/128-inch glass slide was put on each specimen. Finally, with a 500g weight on top of it, the microscopic slide was moved back and forth afew millimeters at about 1 cm/sec for 60 seconds (FIGS. 8( a)-(b)). Theresults showed considerably higher flutax-1 removal from the bare latexcompared to CNT-anchored one (FIGS. 9( a)-(b)). After the test, each ofthe two specimens was dropped in 2 mL of pure ethanol to see if theystill had flutax-1 left on them. There was considerably more flutax-1released (present) from the CNT-anchored latex compared to the bare one(FIG. 10).

A CNT-fitted angioplasty balloon was prepared with vertically alignedCNT arrays and anchored on a polymeric layer. We started with a 20mm-long PET angioplasty balloon (Advance Polymers, Item No. 03002016AA).This balloon was then dipped into a liquid latex compound such that theentire surface of the balloon was covered uniformly with a thin layer oflatex. Before the latex layer was cured, a silicon substrate, which hasas-grown CNTs on it, was placed in the inverted position onto the latexlayer. After the latex layer was cured, the silicon substrate was thenremoved, leaving the CNTs anchored firmly on the latex layer (FIGS. 11(a)-(b)). The right length and packing density of CNTs that allowoptimized drugs delivery and protection can be selected and usedaccording to specific requirements of a particular application.

For continuous monitoring of angioplasty drug delivery,fluorescent-conjugated versions of the drugs intended for delivery, forexample, flutax-1 instead of taxol, can be used. This method eliminatesthe need for potentially hazardous administration of a fluorescent dyeintravenously through a central venous line. Illuminating can be donewith a light source to accommodate the excitation of deliveredfluorescent-conjugated drug. A digital camera can be used to record theimagery of emitted light. (Detter, et al. 2007 Circulation116:1007-1014; Hattori, et al. 2009 Circ Cardiovasc Imaging 2:277-278;Hosono, et al. 2010 Interact CardioVasc Thorac Surg 10:476-477; Tanaka,et al. 2009 J Thorac Cardiovasc Surg 138:133-140; Waseda, et al. 2009JACC Cardiovascular Imaging 2:604-612.)

The following studies apply Fick's second law of diffusion in asemi-infinite medium, x≧0. The concentration at the applicator(angioplasty balloon, etc.) interface is assumed constant in the firstversion, diminishing in the second. The first refers to the initialtime-span when applicator is still touching the plaque, the secondrefers to post applicator removal.

One-Dimensional Semi-Infinite Slab Model of Solid-Solid Diffusion,Version I

This model assumes constant concentration at the applicator (angioballoon, etc) interface, (Perry, et al. 1963 Chemical Engineers'Handbook, 4^(th) edition, McGraw-Hill, Now York.)

$\begin{matrix}{{\frac{\partial{C\left( {x,t} \right)}}{\partial t} = {D\frac{\partial^{2}{C\left( {x,t} \right)}}{\partial x^{2}}}}{{{{Fick}'}s\mspace{14mu} {second}\mspace{14mu} {law}\mspace{14mu} {of}\mspace{14mu} {diffusion}\mspace{14mu} {in}\mspace{14mu} a\mspace{14mu} {semi}\text{-}{infinite}\mspace{14mu} {medium}},{x \geq 0.}}} & (1)\end{matrix}$

Simplified Initial and Boundary Conditions

C(x,0)=0   initial condition (2)

c(0,t)=C ₀   boundary condition (3)

Simplified Analytical Solution

Laplace transform with respect to t yields,

$\begin{matrix}{{{\int_{0}^{\infty}{e^{- {st}}\frac{\partial{C\left( {x,t} \right)}}{\partial t}\ {t}}} = {\left. {D{\int_{0}^{\infty}{e^{- {st}}\ \frac{\partial^{2}{C\left( {x,t} \right)}}{\partial x^{2}}{t}}}}\Rightarrow{\frac{^{2}F}{x^{2}} - {\frac{s}{D}F}} \right. = 0}}{{because}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {initial}\mspace{14mu} {condition}}} & (4) \\{{{{F\left( {x,s} \right)} = {\left( {c_{0}/s} \right)e^{{- {sx}}/D}}},{{F\left( {0,s} \right)} = {c_{0}/s}}}{{because}{\mspace{11mu} \;}{of}\mspace{14mu} {the}\mspace{14mu} {boundary}\mspace{14mu} {condition}}} & (5)\end{matrix}$

Reverse transform yields,

$\begin{matrix}{{{C\left( {x,t} \right)} = {C_{0}\left\lbrack {1 - {\frac{2}{\sqrt{\pi}}{\int_{0}^{x/{({2\sqrt{Dt}})}}{e^{- u^{2}}\ {u}}}}} \right\rbrack}}{{for}\mspace{14mu} {the}\mspace{14mu} {concentration}\mspace{14mu} {peak}\mspace{14mu} {onwards}}} & (6)\end{matrix}$

One-Dimensional Semi-Infinite Slab Model of Solid-solid Diffusion,Version II

This model assumes diminishing concentration at the applicator (angioballoon, etc) interface. (Mehrer 2007 Diffusion in Solids: Fundamentals,Methods, Materials, Diffusion-Controlled Processes, Springer-Verlag,Berlin.)

$\begin{matrix}{{\frac{\partial{C\left( {x,t} \right)}}{\partial t} = {D\frac{\partial^{2}{C\left( {x,t} \right)}}{\partial x^{2}}}}{{{{Fick}'}s\mspace{14mu} {second}\mspace{14mu} {law}\mspace{14mu} {of}\mspace{14mu} {diffusion}\mspace{14mu} {in}\mspace{14mu} a\mspace{14mu} {semi}\text{-}{infinite}\mspace{14mu} {medium}},{x \geq 0.}}} & (7)\end{matrix}$

Simplified Initial and Boundary Conditions

C(x,0)=Mδ(x)   initial condition (8)

where M is the number of diffusing particles per unit area and O(x) theDirac delta function.

$\begin{matrix}{{\frac{\partial{C\left( {0,t} \right)}}{\partial x} = 0}{{boundary}\mspace{14mu} {condition}}} & (9)\end{matrix}$

The analytical solution is the following Gaussian equation

$\begin{matrix}{{{C\left( {x,t} \right)} = {\frac{M}{\sqrt{\pi \; {Dt}}}{\exp \left( {- \frac{x^{2}}{4\; {Dt}}} \right)}}}{{{which}\mspace{14mu} {at}\mspace{14mu} t} = {{0\mspace{14mu} {reduces}\mspace{14mu} {to}\mspace{14mu} {C\left( {x,0} \right)}} = {M\; {\delta (x)}}}}} & (10)\end{matrix}$

The diffusion of drugs from coated anchored CNT arrays and the pressuredriven mass transfer through such structures was experimented withdiffusion of flutax-1 from an anchored CNT array in agar gels andwater-containing protein/lipid/cholesterol structures (including swineand chicken skin). The results indicated that flutax-1 molecules did notmove appreciably in DI water, but do so in agar (in a matter of minutes)or gelatin-water-containing matrices. The results with agar gels arepresented below (FIGS. 12( a)-14(b)), and fit reasonably with the simpletheoretical model. The diffusion from the anchored CNT array wascompared with simple diffusion from a thin strip of dried flutax on abare polymeric sheet (the geometries of both cases examined areillustrated in FIGS. 12( a)-(b).

The diffusion process was modeled with Fick's second law, assumingone-dimensional diffusion and neglecting the melting time of the driedflutax in comparison with the diffusion time within the agar (which issupported by experimental data). Schematic description of the geometryfor both examined cases is presented in FIGS. 15( b) and 15(c).

The model for the case of thin layer of flutax (L₁/L

1) consists of one-dimensional diffusion within the agar gel

${\frac{\partial{C\left( {x,t} \right)}}{\partial t} = {D\frac{\partial^{2}{C\left( {x,t} \right)}}{\partial x^{2}}}},$

and constant concentration C(x=0, t) C₀ and no flux δC (x=0, t)/ox=0boundary conditions at x=0 and x→∞, respectively. A classical solutionfor this problem exists in the literature, and is defined as

${C\left( {x,t} \right)} = {{C_{0}\left\lbrack {1 - {{erf}\left( \frac{x}{2\sqrt{Dt}} \right)}} \right\rbrack}.}$

For the case of flutax positioned within a CNT array (FIG. 15 c) L₂cannot be neglected in comparison with L, and two regions of diffusionare modeled, the agar region and the CNT region. Since the entire lengthof the CNT array is coated with flutax at t=0, the initial condition isnow

${C\left( {x,{t = 0}} \right)} = \left\{ {\begin{matrix}{0,} & {x > L_{2}} \\{C_{0},} & {x < L_{2}}\end{matrix},} \right.$

Utilizing the one-dimensional case, the reduction in available area forthe diffusion process within the CNT region can be modeled by reducingthe value of the diffusion coefficient proportionally to the reductionin surface area and the initial concentration C₀ can be estimated fromthe amount of flutax and the available void space within the CNT array.

FIG. 15( a) presents the numerical solution of the models and theexperimental data for thin flutax layer (squares and smooth line) andflutax within CNT array (triangles and dashed line). The general trendsof the diffusion are predicted reasonably. The main effect of the CNTarray is to change the initial conditions of the diffusion and thus thedifferences between both cases are expected to decrease as t increase,which is indeed observed in experimental data in accordance with themodel.

EXAMPLES Experimental Methods

CNT Arrays Growth.

The vertically aligned multi-walled carbon nanotube arrays used in thisstudy were grown using thermal chemical vapor deposition on siliconwafer substrates. These wafers were coated with 10 nm aluminum oxidebuffer layer and 1 nm iron catalyst layer using electron beam evaporator(Temescal BJD 1800) and diced into 1×1 cm samples. The growth itself wasperformed in a 1-inch diameter quartz tube furnace (Lindberg/BlueMSingle Zone Tube Furnace) under the 490 standard cubic centimeters perminute (seem) ethylene gas (Matheson 99.999%) and 210 seem hydrogen gas(Airgas 99.999%) at a temperature of 750° C. and a pressure of 600 torr.The flow rate and pressure of the gases was maintained by an electronicmass flow controller (MKS πMFC) and a pressure controller (MKS πPC). Theoverall growth quality, including the length of the array, wascharacterized under scanning electron microscope (ZEISS LEO 1550VP).

Anchored CNT on Flat Surface.

A thin layer of uncured polymer (e.g., PDMS) was spin-coated (SCS G3spin coater) onto a flat rigid substrate. The thickness of the polymerlayer can be controlled by varying the speed (rpm) and dwell time of thespinner. As-grown carbon nanotube arrays were manipulated by handlingtheir growth substrate, inverted and then inserted into the spin-coatedpolymer layer. The whole assembly was subsequently cured, usually byheat at elevated temperature (e.g., about 80° Celsius). The CNT's growthsubstrate could then be easily removed after the polymer layer is fullycured. By controlling the polymer layer thickness and CNTs length, thedepth of anchoring of the CNTs into the flexible polymer layer may becontrolled.

Anchored CNT on Balloon.

A 20 mm-long PET angioplasty balloon (Advance Polymers 03002016AA) wasused as a platform. This balloon was then dipped into a liquid latexcompound so that the entire surface of the balloon was covered uniformlyby a thin layer of latex. Before the latex layer was cured. CNTsattached to a silicon substrate were inverted then placed into the latexlayer. The whole assembly was subsequently cured by leaving it in air atroom temperature for 24 hours. After the latex layer was cured, thesilicon substrate was then removed, leaving the CNTs anchored firmly onthe latex layer on the balloon.

Flutax-1 and Uranine Attachment on CNT.

Two types of dye were used in these experiments: the uranine (sodiumfluorescein, Sigma Aldrich 67884) that represents the hydrophilic drugsand flutax-1 (Tocris Bioscience 2226) that represents the hydrophobicdrugs. Since the carbon nanotubes are highly hydrophobic, bothfluorescein sodium and flutax-1 were dissolved in pure ethanol (SigmaAldrich E7023), so that both dyes could wick into the interstices of theCNT specimen. The same amounts of both fluorescein sodium and flutax-1were placed by successively dropping small volumes in each specimen andletting them dry in air at room temperature.

Diffusion Measurement.

Diffusion of flutax-1 from an anchored CNT array was measured in 5% agargels (Sigma Aldrich 17209) in water. The agar gels were placed inside a1450 μm OD×860 μm ID glass capillary tube (Clay Adams 4614). Theanchored CNT array was then placed flush to the tip of the capillarytube. To determine the diffusion profile of the flutax-1 from the CNTarray into the agar gels, time lapsed photographs were taken byfluorescent microscope (Nikon Eclipse TE2000-S). The diffusion profilewas then determined from the fluorescence intensity captured in thesephotographs.

INCORPORATION BY REFERENCE

References and citations to other documents, such as patents, patentapplications, patent publications, journals, books, papers, webcontents, have been made in this disclosure. All such documents arehereby incorporated herein by reference in their entirety for allpurposes.

EQUIVALENTS

The representative examples are intended to help illustrate theinvention, and are not intended to, nor should they be construed to,limit the scope of the invention. Indeed, various modifications of theinvention and many further embodiments thereof, in addition to thoseshown and described herein, will become apparent to those skilled in theart from the full contents of this document, including the examples andthe references to the scientific and patent literature included herein.The examples contain important additional information, exemplificationand guidance that can be adapted to the practice of this invention inits various embodiments and equivalents thereof.

What is claimed is:
 1. The method of claim 1, wherein depositing theagent to the plurality of carbon nanotubes comprises: (i) mixing theagent in a low surface tension solvent forming a solution of the agent;(ii) coating the plurality of carbon nanotubes with the solution of theagent; and (iii) drying the coated plurality of carbon nanotubes,thereby removing the solvent while leaving the agent associated with theplurality of carbon nano tubes.
 2. The method of claim 1, wherein thelow surface tension solvent is an alcohol.
 3. The method of claim 2,wherein the alcohol is ethanol.
 4. An implantable drug delivery device,comprising: (a) an implantable device; (b) an array of carbon nanotubesanchored on the implantable device; and (c) an agent deposited on thearray of carbon nanotubes, wherein the agent is not covalently bound tothe carbon nanotubes.
 5. The implantable drug delivery device of claim4, wherein the agent is a pharmaceutical agent capable of providing atherapeutic effect.
 6. The implantable drug delivery device of claim 4,wherein the agent is a diagnostic agent capable of providing adetectable signal or image indicating a biologically relevant state ofthe subject.
 7. The implantable drug delivery device of claim 4, whereinthe agent comprises an aromatic moiety.
 8. A method for monitoring insitu delivery of an agent, comprising: (a) providing a plurality ofcarbon nanotubes non-covalently associated thereon a pharmaceuticalagent and a second agent capable of exhibiting a spatially detectablesignal; (b) placing the plurality of carbon nanotubes at a targetlocation in the patient's body; and (c) measuring the detectable signalexhibited from the second agent to monitor the deliver of thepharmaceutical agent in situ.
 9. The method of claim 8, wherein theagent is a pharmaceutical agent comprises an aromatic moiety.